Process of sulphonitric attack of arseniureted and/or sulpharseniureted ores or materials, particularly of cobalt and/or of nickel



Oct. 22, 1963 Filed A ril 19, 1956 M. Y. BORVALI ETAL PROCESS OFSULPHONITRIC ATTACK OF ARSENIURE-TED AND/OR SULPHARSENIURETED ORES ORMATERIALS PARTICULARLY 0F COBALT AND/0R OF NICKEL 2 Sheets-Sheet J.

Ore is Crushed to Pass 300 Mesh Comm of Q9 dation Potential Recuperatio'n Addition of of H2804 0nd fs\ Nitrogen Vapors 2' 3 g Crystallizationof 3 AS 0 in the Presv ence of the Residue 5 of the Attack washing ofthe Crystals and Residue i6 Filtration of the As 0 Crystals and i theResidue of the Dissomng f I the Crystals Residue f a [W Attac 9Resuspension of the Filtration to Residue of the Attack Remove the 8 5Residue of Q? q the Attack XF i H "1 DitIusion Dissolution. of As, a d gm E 0 Cl ll l E z gtz g Fe m the i fect Crystalli- Dr in zation of AAddT f B" Oxidation of the z 8203/ t ion a 9 C000 to Neutralt 2 3 izethe Solution I Separation I i (L of the s As Cr stals Separation of theI0 203 y Control of Oxi- As and Fe a ti P te ti as Ferric Arsenate l AsMother INVENTORS. Mehmed Yusuf Barva/r Paul Gral/a Pierre HubscherFrancis Reynaud THE IR A T TORNE Y8 Oct. 22, 1963 9 PROCESS OFSULPHONITRIC ATTACK OF ARSENIURETED AND/OR SULPHARSENIURETED ORES ORMATERIALS, PARTICULARLY OF COBALT AND/OR OF NICKEL Filed April 19, 1956Time in Hours M. Y. BORVALI ETAL 3 107,977

2 Sheets-Sheet 2 300 500 700 900 IIOO Millivolfs Fig. 2

INVENTORS. Mehmed Yusuf Borvali Paul 6/0/10 Pierrg Hubscher Franc/sRey/laud BY u/d, My *hwwlwp THE II? AT TORNEYS United States Patent3,107,977 PROCESS OF SULPHONITRIC ATTACK OF ARSE- NIURETED AND 0RSULPHARSENIURETED ORES 0R MATERIALS, PARTICULARLY OF COBALT AND/ 9R 0FNICKEL Mehmed Yusuf Borvali, Petit-Quevilly, Paul Grolla, Pombliere,Pierre Hubscher, Petit-Quevilly, and Francis Reynaud, Pombliere, France,assignors of two-thirds to Societe dElectro-Chimie dElectro-Metallurgieet des Acieries Electriques dUgine, and one-third to Societe de ProduitsChimiques Bozel-Maletra, both of Paris, France, both corporations ofFrance Filed Apr. 19, 1956, Ser. No. 579,176 Claims priority,application France Apr. 22, 1955 1 Claim. (Cl. 23-144) It is known toattack arseniureted and/or sulpharseniureted ores, particularly ofcobalt and/or nickel, by an acid or an oxidizing acidic mixture, forexample sulphuric acid, nitric acid, or a mixture of the two acids, toobtain the metals contained in the ore as salts in a solution.

The present invention involves a process of placing arseniureted and/orsulpharsenuireted ores or materials, particularly of cobalt and/or ofnickel, in suspension in sulphuric acid and progressively adding nitricacid to oxidize the arsenic and metals. The rate of oxidation iscontrolled by continuously measuring the oxidation potential of thesuspension. At least some of the arsenic in the ore or material isremoved as As O by cooling the suspension.

In the accompanying drawings which illustrate a preferred embodiment ofour invention,

FIGURE -1 is a flow sheet illustrating the present process; and

FIGURE 2 is a typical curve representing the oxidation potentials of theore suspension during the course of the treatment of an ore according tothe present invention. The abscissas designate millivolts and theordinates designate time in hours.

The process according to the invention is carried out in the followingway, which is illustrated, in the case of the treatment of arseniuretedore of cobalt and/or of nickel, by the diagram on FIGURE 1. The ore iscrushed to pass preferably through a 300 mesh sieve (box 1).

The crushed ore is passed (A) to a reactor where it is placed insuspension in sulphuric acid suificient in quantity to transform most ofthe metals into sulphates and provide an excess of acid of about to 40grams per liter. The excess acid maintains the cobalt, and nickel andiron in solution. Nitric acid is introduced, preferably in a continuousmanner, in a sufiicient amount to provide the oxygen required for theoxidation and the concomitant solubilization of the constitutingelements of the ore (box 2). The progress of the oxidation iscontinuously followed, for example, by means of a chain ofplatinum-saturated calomel electrodes immersed in the reactive medium(this control is described in application No. 579,173, filed April 19,1956, now US. Patent No. 2,835,569. The diagram of FIGURE 2 representsan example of this control. The potential increases slowly in the courseof the attack so long as raw ore is still present. When substantiallyall of the reducing materials in the ore have been oxidized anddissolved there is a rapid increase in the potential beginning at pointB of this curve. The addition of nitric acid to the slurry is thenstopped. The lines between points A and B illustrate the minorfluctuation of the potential during the dissolution of the ore.

The object of such a controlled oxidation is to limit the addition ofnitric acid to an amount just suflicient to promote a limited oxidationof the arsenides in the ore. This brings about the complete dissolutionof the e1ements, particularly cobalt, nickel, iron, arsenic, contained3,107,977 Patented Oct. 22, 1963 "ice in the treated material by thesulphuric acid. The object of this limited oxidation is to prepare forthe subsequent separation in the form of AS203 of any excess arsenicpresent which is not necessary to maintain the weight ratio or" iron toarsenic near 1 and which excess thus will not be necessary in thesubsequent formation of ferric arsenate. This control of the potentialalso determines the end of the reaction.

At the time of the oreoxidation, the nitric acid is reduced to a stateof oxygenated compounds of nitrogen, namely, of nitrous vapors. Thesevapors evolve from the suspension and may be collected and regeneratedby the effect of air in an adjacent device (box 3) and used to producethe nitric acid which will be recycled in the operation.

The reaction of the attackbeing ended, the solution is allowed to coolto allow the crystallization of the As O formed (box 4). The solution isthen moved, as shown by C, to a filtration unit where the crystals of A50 and the undissolved residue of the ore are removed simultaneously (box5). The As O crystals and the residue are moved, as shown at D, to bewashed with cold water to eliminate any solubilized cobalt and/or nickeladhering thereto (box 6-). The wash water is removed at S and returnedto be used in forming another suspension of ore (box 2). The-crystalsand residue are then moved, as shown at E, to a dissolving tanlcwherethey are treated with the arsenic mother-water from a precedingoperation of crystallization which will dissolve and extract the As O'from the residue (box 7). The residue from the original acid attack willnot dissolve in this arsenic mother-liquon The solution containing theAS203 and the residue of the acid attack is then moved (F) to afiltration unit where it is filtered and the residue (which is retainedon the filter) is washed with boiling water to extract therefrom any AsO with which it was still impregnated (box 8). The residue of the acidattack is removed at G to box 12 for further processing which will bedescribed hereinafter. The filtrate which contains only As O is removedat H to a cooling unit to allow the crystallization of the As O (box 9).Normally the solution is cooled to a temperature below 25 C. to'allowproper crystallization. The wash water from the filtration in box '8 isjoined with this original solution containing the As O This combinedsolution contains about grams of As O per liter. The solution is moved(I) to a unit for the separation of pure wet As O crystals (box 10).These wet As O' crystals are moved (K) to a drying unit and there dried[for ultimate sale (box 11). The dried crystallized As O is 99.8% pure.

The arsenic mother-liquor which is the filtrate from box 10 leaves box10 as shown at M and is returned to box 7 for the dissolution of thenextbatch of AS203 crystals.

The solution coming from box 5 as shown at L contains substantially allof the cobalt, nickel and iron contained in the initial ore and anyarsenic which was not crystallized out as AS203.

The residue G coming from the filtration of box 8 is now tree from As Obut still contains 1.5 to 2% cobalt and nickel and the noble metals, ifthere were any in the starting ore. It the residue G does not containany precious metals, it may be thrown away. But if further processing isadvisable or desirable, owing to the presence of precious metals forexample, this residue G is resuspended in the solution as shown in box12.

The suspension is then moved as shown at R to the next step illustratedin box 13 which is the dillu-sion of chlorine into the solution. Thechlorine solubilize-s the cobalt, nickel and the arsenic which are stillin the residue in the form of unattacked arsenides, oxidizes the arsenicinto arsenic acid and dissolves and maintains in solution the preciousmetals.

Calcium carbonate is subsequently added to this oxidized solution toneutralize the latter and precipitate'the arsenic and iron as ferricarsenate. A 1 to 1 weight ratio is necessary between the arsenic andiron at this point to properly precipitate ferric arsenate. Thenecessary control of the oxidation potential and a complete descriptionof this portion or the process are shown inside box X and are fullydescribed in patent application No. 579,173, filed April 19, 1956, nowUS. Patent No. 2,835,569. I

The process according. to the invention provides, not only for therecovery of the arsenic as substantially pure AS203, but a simple andconvenient control of the acid attack on the ore and a continuousoperation.

Example 500 kilograms of a row smaltine of a composition comprisingsubstantially: Co='.82%, As=52.8%, Fe: 8.14%, Ni=l. 14%, and Au='l3.8grams per metric ton, were put in suspension in 400 liters of wash watercoming from a preceding operation (S). 200 kilograms of sulphuric acid,calculated as a monohydrate (box 2), were then added.

A portion of the suspension, contained in the reactor, was continuouslyremoved therefrom and sent to a measurement cell in which were immerseda chain of platinumsa turated calornel electrodes connected with ameasurernent amplifier followed by a registering device. The sampleliquid was returned to the reactor. Nitric acid at 36 Be. was then addedat the rate of 200 liters per hour. The heat generated by the reactionwas sufficient to maintain the temperature of the medium at a value ofabout 95 centigrade. The oxidation potential rose slowly from 300millivolts to about 500 millivolts. At this latter value, the potentialrapidly increased to about 800 millivolts and remained there. At thatmoment, the addition of nitric acid was stopped.

The total amount of nitric acid added was 550 liters:

and the reaction lasted about three hours.

The solution was :allowed to cool and was then filtered. 900 liters offiltnate was obtained which was placed aside for later use.

The crystallized products and the acid attack residue on the filter werewashed with cool water to remove any cobalt or nickel which had adheredthereto, and the wash water was put aside for use in another operationof the process. The crystallized product was again put into suspensionfor two hours in 5400 liters of arsenical rnother- 'water (M) at 100centigrade. The arsenical motherwater initially contained 25 gnams of AsO per liter of solution. This solution dissolved the As O crystals butdid not dissolve much of the residue of the attack.

This solution was then filtered when hot and the attack residue whichwas retained on the filter was washed with 250 liters of water at 100centigrade. The wash water was joined with the filtrate from thefiltration step. The residue on the filter was dried and weighed. 120kilograms of dry product was obtained which contained about 0.9% cobalt,thus indicating a solubilizia-tion yield of 98% cobalt.

The combined filtrate and wash water were allowed to cool and thuscrystallization of the A5 0 was brought about. Upon centrifuging thissolution, 295 kilograms of crystallized As O were obtained.

The dearsenated residue (G) of the attack left on the filter was thenput in suspension in the initial motherwater which had previously beenplaced aside from box 5. The temperature of the suspension was broughtto C. and chlorine was diffused through it. Control of the oxidationpotential was maintained by a chain of platinum-saturated calomelelectrodes, until all the elements present in the medium were at theirmaximum valance and a slight excess of chlorine was present. Theappearance of excess was revealed by a sudden increase in the oxidationpotential. The potential was then stabilized at a value slightly above1000 millivolts and maintained there for three hours to dissolve thegold.

The suspension was then filtered and the residue washed. The dry weightoat the residue on the filter was kilograms and was comprised of 0.19%cobalt and 3.2 grams of gold per metric ton.

99.65% of the cobalt and 95.35% of the gold had been solubilized.

Calcium carbonate was added to the filtrate and the oxidation potentialwas controlled as described in application No. 579,173, filed April 19,1956, now US. Patent No. 2,835,569. The arsenic and iron were thusprecipitated as fer-ric arsenate. The solution was then furtherprocessed to recover the metals from it.

The invention is notlimited to the preferred embodiment but might beotherwise embodied or practiced within the scope of the following claim.

We claim:

A one-step process of extracting arsenic from arseniureted andsulfarseniureted ores containing nickel, cobalt and large amounts ofarsenic, which process consists essentially of introducing said ore inpowdered form into a sulphuric acid solution; said sulphuric acid beingpresent in an amount slightly inexcess of the amount. sufficient todissolve said nickel and cobalt; said process being performed atatmospheric pressure and about room temperature; therearfter slowly andprogressively adding only nitric acid to said solution with continuousagitation;

continuously controlling the addition of nitric acid to maintain theoxidation potential of the solution solely in the limited range 300-500millivo'lts during the nitric acid addition until substantially all ofthe metals inthe ore are dissolved and substantially all the arsenic inthe ore is oxidized to arsenous oxide; stopping the nitric acid additionas soon as the oxidation potential of the solution suddenly increases toa value greater than 500 millivolts; cooling the solution to crystallizeout only the arsenous oxide; filtering the solution to remove a solidcontaining the crystallized arsenous oxide and any insoluble residue ofthe ore trom a filtrate; further processing the filtrate to remove themetals therefrom, and the solid to separate arsenous oxide therefrom.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Latimer in The Oxidation States of the Elements and 3 TheirPotentials in Aqueous Solutions, published by Prentice-Hall, Inc, NewYork, 1938, pp. 2, 3 and 103- 107.

